Mixture yielding thermally stable photo-cross-linkable layers and foils

ABSTRACT

The invention provides mixtures based on resins containing allyl groups and being solid at room temperature, useful for the preparation of thermally stable, photo-crosslinkable layers and foils. According to the invention, such mixtures comprise triallylcyanurate prepolymers and/or triallylcyanurate precopolymers with compounds containing allyloxy and/or allylester groups, and compounds with at least one N-maleimide group, wherein the C═C double bond of the N-maleimide groups are bonded to hydrogen, hydrogen and chlorine or hydrogen and methyl radicals. Preferably, the N-maleimide C═C bonds carry hydrogen.

BACKGROUND OF THE INVENTION

This invention is concerned with mixtures yielding thermally stable,photo-crosslinkable layers and foils based on resins which contain allylgroups and are solid at room temperature, useful for the photographicpreparation of layered structures.

Light-sensitive compositions based on inert organic polymeric bindingagents, thickening agents or matrices and acrylic or methacryliccompounds are known in the art from German Auslegeschriften Nos.1,205,386, 1,200,130, and 1,915,571 and form GermanOffenlegungsschriften Nos. 1,906,668 and 2,149,056. These compositionsare partly usable in foil form for the generation of patterns andstructures. The layered structures that can be produced from thesecompositions have only limited thermal stability. In addition,relatively high concentrations of the photo-reactive acrylic ormethacrylic compounds are necessary for producing high lightsensitivity. This leads to sticky photosensitive layers which, when usedin common photographic techniques with contact copies, must be exposedthrough protective films. Since the pattern and the photosensitive layerare not in direct contact with each other, inferior resolution resultsdue to light diffraction.

Furthermore, thermally stable, photo-crosslinkable materials having aresin component containing allyl groups are known according to U.S. Pat.No. 3,462,267 and South-African Patent No. 05209. The materialsdescribed therein however have the common disadvantage that layershaving a thickness of no greater than about 1 to 5 μm have sufficientlight sensitivity, but with increasing layer thicknesses the lightsensitivity diminishes. It is further known from German Patent No.2,130,904 that certain photo-cross linkable systems exhibitcross-linking speeds with layer thicknesses of more than 10 μm and thesemake possible the preparation of layered structures with sharp contoursand good insulating properties. These systems consist of a prepolymercomponent containing carboxylic acid allylester groups and compoundscontaining maleimide groups. A limiting effect for many applications ofsuch systems is the limited thermal stability of the describedprepolymer components.

It has now been found according to the present invention thatsurprisingly the ring-positioned allyloxy groups of triallylcyanurateprepolymers in combination with compounds containing N-maleimide groups,if exposed to actinic light, give high crosslinking speeds at layerthicknesses of more than 10 μm. The light-sensitive mixtures accordingto this invention, yield layers and films for the photographicpreparation of thermally stable layered and film structures having sharpcontours and of crosslinked coatings with good insulating properties.

SUMMARY OF THE INVENTION

According to the present invention, the mixtures comprisetriallylcyanurate prepolymers and/or triallylcyanurate precopolymerswith compounds containing allyloxy and/or allylester groups andcompounds containing at least one N-maleimide group whose maleimide C═Cbond carries hydrogen, hydrogen and chlorine or hydrogen and methylradicals, but preferably, hydrogen.

The photo-crosslinked coatings from these compositions obtained throughthe action of actinic light or the exposed photographic copies which canbe produced with sharp contours by solvent etching, are distinguishedparticularly by their high thermal stability, in addition to theirinsulating properites, i.e., high aging stability, high electric surfaceand bulk resistance, low water absorption and swelling.Thermogravimetric analysis shows that the materials still have excellentstability at 300° C; with a heating rate of 5° C/min in air, a weightloss of 0.5%/min occurs at 300° C and the color of the material remainsunchanged. The weight loss of relatively heat-stable systems inaccordance with German Patent No. 2,130,904 usingpolydiallylorthophthalate as the resin component containing carboxylicacid allylester groups, is higher by a factor of 6 at 300° C, and at thesame time, the material is discolored black. To the extent that handlingrequires, the materials according to the present invention aresolder-bath proof and mechanically stable, and also exhibit at least a140° C fatigue strength in air.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

As components of the mixtures according to the invention containingallyloxy groups, film-forming triallylcyanurate prepolymers andprecopolymers of triallylcyanurate with compounds containing allyloxy-and/or allylester groups are suitable such as, phenylallylether,bisphenol-A-bisallylether, benzoic acid allylester, diallylphthalate,diallylisophthalate or diallylterephthalate, which can be prepared bymethods known in the art from triallylcyanurate and other comonomers bypolymerization up to a period shortly before gelation and by subsequentseparation into soluble polymer or copolymer fractions and a monomerfraction, for instance, according to U.S. Pat. No. 3,030,341.

Suitable components of the mixtures according to the inventioncontaining N-maleimide groups are aliphatically, aromatically orheterocyclically nitrogen-substituted maleimides, 3-chloromaleimides,3-methylmaleimides such as, N-cyclohexylmaleimide, N-phenylmaleimide,N-phenylmaleimide substituted at the benzene nucleus (Preferredsubstituents have alkyl groups in the o-position) as well as compoundshaving two or more N-maleimide groupings, as are obtained from thecorresponding polyfunctional amines, such as, for instance,hexamethylene diamine, m-phenylene diamine, p,p'-diaminodiphenyl orp,p'-diaminodiphenylmethane in a known manner by reaction of thesecompounds with maleic acid anyhdride. Preferably, N-arylmaleimides areused. N-aryl-maleimides, alkyl-substituted in the ortho-position, suchas, for instance, N-o-tolylmaleimide, have been found particularlysuitable.

The properties of the mixtures according to the invention can further bemodified, in the kind and content of comonomer components of thetriallylcyanurate prepolymers, by components of polymers compatible withpolytriallylcyanurate. Thus, the addition of polyester resins bringsabout increased flexibility. Particularly suited are portions ofunsaturated polyester resins, i.e., polymers containing maleate and/orfumarate structure elements. Surprisingly, it has been found that theseunsaturated polyester resins degrade the original light sensitivity ofthe mixture of triallylcyanurate prepolymers with compounds containingN-maleimide groups only inappreciably or not at all. Accordingly, theconclusion may be drawn that the maleate or fumarate double bonds of theunsaturated polyester resins copolymerize upon exposure to light withthe photoreactive allyloxy- and/or maleimide groups and thus participatein the cross-linking reaction and in the process also change thesolubility of the polyester resins. Thus, excellent edge sharpness andhigh resolution can be achieved also in the presence of the unsaturatedpolyester resins. The content of unsaturated polyester resins may be upto 50% by weight; preferably, 5 to 30%. The ratio of the allyl doublebond equivalents, and as the case may be, including the maleate and/orfumarate double bond equivalents of unsaturated polyester components, tothe N-maleimide double bond equivalents is equal to or greater than 1,and preferably 2 to 150. Preferably used are unsaturated polyesterresins with an acid number smaller than 25 and preferably smaller than10. The polyester resins are prepared by known polyaddition orpolycondensation methods (see, for instance, the book by J. Bjoerkstenet al., Polyesters and their Application, Reinhold PublishingCorporation, New York, 1956). Many unsaturated polyester resins usefulin the present invention are available as commercial products.

The cross-linking speed can be increased further by the addition ofsuitable photosensitizers and/or initiators, preferably in percentagesof less than 2% by weight.

Highly suited as sensitizers and/or initiators are, for instance,Michler's ketone and/or benzoinether, 2-tert-butyl-9, 10-anthraquinone,1, 2-benz-9, 10-anthraquinone, 4, 4'-bis-diethylamino)-benzophenone.

The mixtures according to the invention can be dissolved in inertorganic solvents, applied to a substrate, e.g., a film, and cross-linkedby exposure to actinic light after the solvent has evaporated. Bypattern-wise exposure through a copying pattern and subsequent solventtreatment, copies with sharp contours are obtained.

The mixtures according to the invention can further be adjusted bycomponents of up to 20% by weight of low-molecular to oligomeric,preferably liquid to viscous, olefinically-unsaturated compounds,preferably methacrylic, acrylic, vinyl, allyl, maleic acid or fumaricacid compounds, so that they can still be calendered and extruded attemperatures below 100° C down to room temperature and can therefore beprocessed in a technically advantageous manner into self-supportingpolymer films or photopolymer films embedded between protective films.Suitable compounds are, for example, ethylene glycolbismethacrylate or-acrylate, diethyleneglycolbismethacrylate or -acrylate,trimethylolpropane trimethacrylate or -acrylate, glycerintrismethacrylate or -acrylate, 1,3-propanediolbismethacrylate or-acrylate, 1,2,4-butane trioltrimethacrylate or -acrylate, hydroquinonebismethacrylate or -acrylate, pentaerythritol tetramethacrylate or-acrylate, polyethyleneglycol bismethacrylate or -acrylate havingmolecular weights of 200 to 500, divinylsuccinate, divinylphthalate,allylbenzoate, diallylphthalate, maleic acid or fumaric aciddiethylester. Methacrylic compounds are preferred.

Preferably, contents of between 5 and 10% by weight are used. Thephotopolymer films or foils obtainable in this manner are flexible, nonsticky and can be exposed for generating patterns or structures throughprotective foils as well as, for direct contact with the pattern whichis preferable. Subsequent solvent treatment then yields patterns andstructures with particularly sharp contours. The additions do notadversely effect the light sensitivity of the photopolymers and thethermal stability of the photo-crosslinked layered structures.

The ready-to-use solutions of the photo-crosslinkable mixtures accordingto the invention and the ready-to-use films and foils prepared from themixtures according to the invention have a high storage stability ofmore than 1/2 year at room temperature, if protected from light.

The mixtures according to the invention can be crosslinked by exposureto actinic light of any origin and kind as well known in the art.

The mixtures according to the invention contain components which arereadily available and can be produced inexpensively and can betransformed by simple means into heat-resistant insulating layers,insulating layer structures and images. The adhesion of the layers,layer structures and images produced on different substrates can befurther improved by commonly used adhesive agents such as, theorgano-silicon compounds, i.e., vinyltriethoxysilane,vinyltrimethoxysilane, γ-methacryloxy-propyltrimethoxysilane andparticularly, by 2,4-diallyloxy-6-[3-(triethoxysilyl)propyl]aminotriazine. They can be provided in a known manner with seed layersfor generating highly adhering electro-deposits. The conditions for awide and technically advantageous application of the photocrosslinkedinsulating materials therefore exist. The mixtures according to theinvention are generally suited for the applications described in theGerman Patent No. 2,130,904 and in addition, particularly for thepreparation of thermally stable patterns and insulating, passivating andother protective layers and layered structures, especially as in aid inthe manufacture or as part of components and circuits inelectrotechnology, such as, solder protection layered structures oncircuit boards for passivation structures on semiconductor components oreasily removable photoresists for evaporation, sputtering, implantationand diffusion, ion-etching and other etching processes and forelectroplating processes in the manufacture of semiconductor components.

The invention will be explained in further detail in the followingexamples:

EXAMPLE 1

Preparation of a triallylcyanurate prepolymer.

Exactly 800 parts by weight triallylcyanurate were dissolved in 800parts by volume xylene and reacted at 90° C with 40 parts by weight of a50-% benzoylperoxide paste, while stirring.

After the exothermic reaction had died down, stirring was continued at130° C until the reaction solution had a viscosity of about 65 [10³Ns/m² ]. From the cold reaction solution, the prepolymer wasprecipitated by dropping-in 6000 parts by volume isopropanol and dryingunder a vacuum at 50° C. The yield was 45%. The product had 0.64double-bond equivalents per 100 g and will be designated in thefollowing as PTAC.

Exactly 50 parts by weight PTAC, 3.75 parts by weightN-cyclohexylmaleimide and 0.5 parts by weight Michler's ketone weredissolved in 200 parts by volume trichloroethylene. The solution wasfiltered and centrifuged on glass substrates to form uniform films,which were 15 μm thick after the solvent had evaporated.

The films were exposed through a contact pattern for 20 sec to a 500-W(Very-high-pressure) mercury lamp placed at a distance of 23 cm from thefilms. Subsequently, well-adhering structures with sharp edges and highresolution (better than 20 μm) were produced by immersion in1,1,1-trichloroethane for 2 minutes and a mixture of1,1,1-trichloroethane and trichloroethylene (2:1) for 5 sec and washingwith isopropanol. The film structures withstood the usual solder bathtemperature of 260° C for 30 sec without damage. The electric bulkresistance of the crosslinked, hardened films, measured in accordancewith DIN 53482, was higher than 10¹⁴ ohm-cm, and the dielectricconstant, measured in accordance with DIN 53483, was about 3 at 10³ Hz.

EXAMPLE 2

Exactly 50 parts by weight PTAC, 3.75 parts by weight N-phenyl maleimideand 0.5 parts by weight Michler's ketone were dissolved in 200 parts byvolume trichloroethylene and, as described in Example 1, centrifuged onaluminum foil to form films 15 μm thick, exposed for 20 sec anddeveloped to form structures with sharp contours, great adhesitivity andresolution (better than 20 μm). The film structures withstood the usualsolder bath temperature of 260° C for 30 sec without damage. Theelectric bulk resistance of the crosslinked hardened films was higherthan 10¹⁴ ohm-cm as measured in accordance with DIN 53482 and thedielectric constant was about 3 at 10³ Hz, as measured in accordancewith DIN 53483.

EXAMPLE 3

Exactly 50 parts by weight PTAC, 3.75 parts by weight N-phenylmaleimide,0.5 parts by weight Michler's ketone and 5 parts by weight2,4-diallyloxy-6-[3(triethoxysilyl)propyl] aminotriazine were dissolvedin 1000 parts by volume of trichloroethylene and processed bycentrifuging on silicon wafers with an oxide surface to form films 1 μmthick. By centrifuging a solution of 50 parts by weight PTAC, 3.75 partsby weight N-phenyl maleimide, and 0.5 parts by weight Michler's ketonein 200 parts by volume trichloroethylene, films 15 μm thick were thenapplied to the thin films. By exposing and developing as in Example 1,similar structures with sharp edges were produced, which hadparticularly good adhesion.

EXAMPLE 4

Exactly 50 parts by weight PTAC, 3.75 parts by weight o-tolylmaleimide,0.5 parts by weight Michler's ketone and 0.5 parts by weightbenzoinisopropyl ether were dissolved in 200 parts by volume toluene andcentrifuged on Al₂ O₃ ceramic substrates to form films 15 μm thick. Asdescribed in Example 1, the films were exposed for 10 sec through acontact-copy pattern and developed. The highly adhering layer structureswith sharp contours withstood the usual solder bath temperature of 260°C for 1 min without damage. The electric bulk resistance of thecrosslinked, hardened films was above 10¹⁴ ohm-cm, measured inaccordance with DIN 53482, and the dielectric constant, as measured inaccordance with DIN 53483, was about 3 at 10³ Hz.

EXAMPLE 5

Exactly 50 parts by weight PTAC, 3.75 parts by weight o-tolylmaleimide,0.5 parts by weight Michler's ketone, 0.5 parts by weightbenzoinisopropyl ether and 0.5 parts by weight2,4-diallyloxy-6-[3(triethoxysylil)propyl] aminotriazine were dissolvedin 200 parts by volume toluene and centrifuged on Al₂ O₃ ceramicsubstrates to form films 15 μm thick. By exposing and developing as inExample 4, corresponding layered structures with sharp contours wereproduced which exhibited particularly good adhesion.

EXAMPLE 6

Exactly 40 parts by weight PTAC, 10 parts by weight of a polyester resinwith the acid number 20, containing the components fumaric acid,isophthalic acid and neopentylglycol in the mole ratio of 2:3:5, 3.75parts by weight o-tolylmaleimide, 0.5 parts by weight Michler's ketoneand 0.5 parts by weight benzoinisopropyl ether were dissolved in 200parts by volume xylene, centrifuged on a 50- μm Cu foil to form films 15μm thick and converted, as described in Example 1, into layeredstructures with sharp contours by exposing and developing. Theelasticity and adhesion of the scratch-proof layers were demonstratedfrom the bending mandrel test according to DIN 53152. With a bendingmandrel diameter of 2 mm, neither cracks nor flaking-off appeared, andlikewise by crinkling the coated foil. The electric bulk resistance ofthe crosslinked films, measured in accordance with DIN 53482, was higherthan 10¹⁴ ohm-cm and the dielectric constant, as measured in accordancewith DIN 53483, was about 3 at 10³ Hz.

Epoxy resin circuit boards with a final copper and tin surface weresprayed by means of a spray gun with the solution above and in thismanner coated with films 30 μm thick. After exposing 30 sec through acontact copy in a Gyrex printer 900, developing and washing as inExample 1 and drying of the boards at 120° C for 30 min, perfectlysoldered circuit boards with the solder resist layers intact wereobtained in a wave soldering operation at 260° C. Similar results wereobtained when the solution above contained additionally as apigmentation component, 0.1 parts by weight Viktoria blue BOD Type 1246(neutral) of the firm BASF.

EXAMPLE 7

Exactly 80 parts by weight of PTAC, 20 parts by weight of a polyesterresin with the acid number 20, containing fumaric acid, isophthalic acidand neopentylglycol in the mole ratio 2:3:5, 7.5 parts by weighto-tolylmaleimide, 0.5 parts by weight Michler's ketone, 0.5 parts byweight benzoiniospropyl ether and 10 parts by weightdiethyleneglycolbismethacrylate were mixed in a calender at roomtemperature and then calendered at 90° C to form sandwich foils with apolyethylene carrier and polyethylene terephthalate cover foils of 20 μmand a photoreactive intermediate layer of 60 μm.

After the carrier foil was pulled off, the sandwich foils were led overa cylinder with a temperature of 90° C and laminated onto epoxy resincircuit boards with a final copper or tin surface.

Part of the circuit boards was exposed in the Gyrex printer 900 throughnegative copy, which was in close contact with the cover foil, for 40sec and developed as described in Example 1.

In another part of the coated circuit plates, thepolyethyleneterephthalate cover foil was pulled off and the exposure wascarried out with close contact between the negative copy and thephotoreactive layer. In the latter case, structures with considerablysharper contours resulted. The solder resist layers withstood thesubsequent wave solder operation at 260° C without change. The electricbulk resistance of these layers, measured in accordance with DIN 53482,was above 10¹⁴ ohm-cm and the dielectric constant, as measured inaccordance with DIN 53483, was about 3 at 10³ Hz.

What is claimed is:
 1. A composition comprising a mixture of;a. atriallyl cyanurate prepolymer and/or a precopolymer of triallylcyanurate with a compound containing a radical selected from the groupconsisting of allyloxy, allylester and mixtures thereof; and b. acompound containing at least one N-maleimide group wherein the C═Cdouble bond of the N-maleimide group is bonded to two radicals selectedfrom the group consisting of hydrogens, hydrogen and chlorine, andhydrogen and methyl.
 2. The composition of claim 1 wherein the C═Cdouble bond of said N-maleimide group are bonded to two hydrogens. 3.The composition of claim 1 wherein the N-maleimide group is an N-arylmaleimide.
 4. The composition of claim 3 wherein the aryl group of saidN-aryl maleimide is substituted by an alkyl group in the ortho position.5. The composition of claim 4 wherein said N-aryl maleimide isN-o-tolylmaleimide.
 6. The composition of claim 1 which furthercomprises soluble olefinically unsaturated polymers.
 7. The compositionof claim 1 wherein the ratio of allyl double bond equivalents tomaleimide double bond equivalents is at least
 1. 8. The composition ofclaim 7 wherein the ratio is from about 2 to
 150. 9. The composition ofclaim 6 wherein the ratio of allyl double bond equivalents and solubleolefinically unsaturated polymer double bond equivalents to maleimidedouble bond equivalents is at least
 1. 10. The composition of claim 9wherein the ratio is from about 2 to
 150. 11. The composition of claim 6wherein the soluble unsaturated polymers are unsaturated polyesterresins.
 12. The composition of claim 11 wherein the unsaturatedpolyester resins contain elements selected from the group consisting ofmaleate, fumarate and mixtures thereof.
 13. The composition of claim 11wherein the acid number of the unsaturated polyester resin is less than25.
 14. The composition of claim 1 which further comprises a photoinitiator or photosensitizer in an amount by weight no greater than 2%based on the weight of all components of the mixture.
 15. Thecomposition of claim 1 which further comprises up to 20% by weight basedon all components of the mixture of a copolymerizable olefinicallyunsaturated compound, said compound being of low molecular weight tooligomeric and having a consistency of liquid to viscous.
 16. Thecomposition of claim 15 wherein said olefinically unsaturated compoundscomprise from 5% to 10% by weight based on all components of saidmixtures.
 17. The composition of claim 15 wherein the olefinicallyunsaturated compounds are methacrylic compounds.
 18. A process for thephotographic preparation of patterns and for the preparation ofprotective layers and layered structures comprising:a. forming a film orfoil of the composition of claim 1 on a substrate; b. pattern wiseexposing said film or foil to actinic radiation; and c. developing saidfilm or foil.
 19. The process of claim 18 wherein the exposing takesplace in direct contact with the copying pattern.